In U.N. Showdown, Russian Veto Kills Syria Chemical Arms Panel

“There was nothing balanced in the U.S. resolution,” Mr. Nebenzia said. Later he told reporters waiting outside the Security Council chambers that Russia “condemns the use of chemical weapons by anyone” but that the panel’s reporting was “a joke — complete nonsense.”

It was the 10th time Russia had used its veto power as a permanent member of the Security Council to protect the Syrian government, its principal ally in the Middle East.

The veto threw into doubt whether those responsible for chemical weapons use in Syria will ever be held to account. The bitter differences expressed by the United States and Russia, reminiscent of the Cold War, also called into question whether they can cooperate more broadly on ways to end the Syria war, which is nearly seven years old.

Eleven of the 15 members of the Security Council voted in favor of the American resolution, with Russia and Bolivia opposed, and China and Egypt abstaining.

After a short recess, the council reconvened to vote on an alternate resolution drafted by Russia to extend the panel’s mandate, under conditions that the United States and its allies said would have eviscerated its abilities. That resolution received four yes votes — far below the nine needed for passage.

Russia has expressed deep anger over the panel’s Oct. 27 report, which found that the Syrian military had been responsible for a deadly sarin attack on the village of Khan Sheikhoun in northern Syria on April 4.

Panel investigators relied on interviews, photos, videos and analysis of soil samples, including those supplied by the Syrian government from Khan Sheikhoun. They did not go to the attack site because of security concerns.

Calling the report deeply flawed, riddled with inconsistencies and tainted by Western pressure to vilify the Syrian government, the Russians rejected the findings and suggested that Syrian insurgents or Islamic militants might have staged the attack.

The United States and its allies strongly defended the panel’s integrity and professionalism, accusing Russia of trying to neuter its ability to identify who is behind chemical weapons attacks in Syria.

Hours before the Security Council voting, Russia’s foreign minister, Sergey V. Lavrov, had signaled at a Moscow news conference that his country intended to block the American-drafted resolution.

Mr. Lavrov said the panel’s investigators had shown themselves to be “biased, politicized” and “clearly carrying out orders from the outside.”

The American resolution, he said, “aims to extend the mandate of this mechanism by welcoming and approving the methods that it uses.”

“It is clear that this is absolutely unacceptable,” Mr. Lavrov said.

The chemical weapons panel, known as the Joint Investigative Mechanism or J.I.M., was a collaboration of the United Nations and the Organization for the Prohibition of Chemical Weapons, which monitors compliance with the treaty banning them.

The panel required a new Security Council mandate to continue working beyond 11:59 p.m. Thursday, the expiration of its current mandate.

The panel’s leader, Edmond Mulet, a veteran United Nations diplomat, said in an interview last week that it had been forced to wind down investigations of other possible chemical attacks in Syria because of the uncertainty. How, or even whether, the perpetrators of those attacks will be identified is now unclear.

Dissolution of the panel nullifies an important area of cooperation between Russia and the United States in Syria, despite their bitter differences over who is to blame in the conflict.

Chemical weapons disarmament experts, who welcomed the creation of the investigative panel two years ago, also expressed alarm about its demise, saying that it sends a signal to chemical weapons users that they could act with impunity.

“It is very important that the J.I.M. investigations go forward,” said Paul F. Walker, director of environmental security and sustainability at Green Cross International, a disarmament advocacy group.

Mr. Walker, who has worked with inspectors from the Organization for the Prohibition of Chemical Weapons for many years, also rejected Russia’s criticism of the Syria panel.

“I am fully convinced that their work is very professional, unbiased, and based on forensic evidence, witness interviews, laboratory analysis and available intelligence,” he said.